I would recommend to your client you will qualify a pqr and subsequent wps using ASME Sec. IX for reference and direction. Moreover, be specific in noting in qualification that 4140 is an unassigned P number with no ASME base metal affiliation.

Mr. Dibben:

In the ASME WPS that I have prepared involving 4140 material we specified the AISI specification, as the P number was not required. As to which P number it is, I do not have a recent ASME code to check. I don't think it is assigned a P number as it is in between a P3 and P4 material. However, have you tried looking up the P number up using its UNS designation?

4140 is a SAE (Society of Automotive Engineers) designation, which has nothing to see with ASME (American Society of Mechanical Engineers) designations, so you CAN NOT assign a P number to it, because P numbers apply specifically to ASME steels.
If your client is a large company and has an engineering department they should agree with this.
In any case, if you want to assign a P number to SAE 4140 at any cost, I suggest that you do what Sean says: check whether SAE 4140 has a UNS number and whether an ASME steel has the same number. In this case you can say that, after having done a research, you have concluded that, BY ANALOGY, the P number of SAE 4140 MAY BE ASSIMILATED TO ......... (whatever it is), but that THIS IS ONLY AN APPROXIMATION and YOU ARE NOT RESPONSIBLE for whatever consequences might arise from that statement.
Giovanni S. Crisi
Sao Paulo - Brazil

Hi H.Dibben

In South Africa we often weld steels made to European and South African specifications with the ASME IX code. This has lead to many debates regarding P number classifications. At the end of the day I believe that you can only really follow the ASME IX code to the "letter of the law". As such, if you weld any steel not specifically assigned a P number in the code, then it must be given a P number designation of:

"unassigned"

This means that in future you must quality this unassigned material to itself as well as making seperate test pieces to qualify the "unassigned" material to any other unassigned material as well as making seperate test peices to qualify the unassigned material to any assigned material.

In total, this starts costing money, but then you are totally "covered" in the event that something goes wrong, WHICH IT WILL, given enough time.

It is for this reason that I preffer the approach taken by a code such as EN 288. According to this code, you classify the material yourself, into the relevant classification based on their guidelines.

Just remember that when it comes to welder (personnel) qualifications, then ASME IX gives you more leeway. In essence it states that any material that is "equivalent" to a particular P number material can also be welded by the welder that was qualified to that P number.

In short: You can weld 4140 steel to ASME IX, and you can assign it a P number of "unassigned", as long as you follow the code rules.

Having said this, we must also not go around in life so narrow minded that we can look through a keyhole with both eyes at the same time! If we are constructing "non-critical" components that are not required by law to be restricted to any particular design, fabrication or welding code, but want to follow a sound welding "guideline" to ensure the product quality, then you have more flexibility. Under these circumstances, you are totally free to write something like "equivalent to P 4" on the welding procedure or PQR, because technologically it is no different than welding that P number. (I use the P number here as an example, not saying that it is equivalent!) You just can't use this PQR to back a WPS for welding a pressure vessel.

Hope this reasoning makes sense.

Regards
Niekie Jooste
Fabristruct Solutions